Put the water in a sauce pan over high flame until boiling; add the onions. Cover, lower heat to medium, and cook 5 minutes. Whisk in all the other ingredients (except for the spinach); when gently bubbling, stir in the frozen spinach. Cook 8 minutes, stirring every 2 minutes. Lower flame if sticking or burning. Serve with anything. This is so delicious that it can be the centerpiece of a vegetarian meal. May be used as a dip when cool.